Environmental and industrial hygiene samples originate from air, water, soil and surfaces from places such as, industrial sites, waste storage, dumps and those that may have been contaminated by other human and natural activities. Some of the toxic industrial materials are lead, hexavalent chromium, cadmium, mercury and beryllium to name a few prominent ones. These materials are typically analyzed by extracting the toxin or the contaminant in a liquid medium (using acids, bases and other solvents and solutions) and then subjecting this to analysis. The liquid extraction ensures that the samples are captured in a homogenous matrix. Typical analysis involves taking these samples and analyzing them sequentially through chromatography (e.g., high performance liquid or gas chromatography), inductively coupled plasma along with atomic emission or a mass spectrometer (ICP-AES and ICP-MS respectively). All the samples to be analyzed are eluted into the equipment in a sequence with enough gap or purge so that there is no cross-contamination. To decrease the labor content and increase the efficiency of the analysis, autosamplers have been developed for such instruments. In these, the samples are put in a queue and are automatically analyzed one after the other. As an example in modern ICP-MS instruments, 200 samples may be queued which can take 10 hours to analyze. The long analysis time not only limits the throughput, but can cause drift in baseline, and for proper quantification it is customary to run calibration standards periodically, which means more sample preparation and more delay in getting the results. Laser induced breakdown spectroscopy (LIBS) is being used increasingly to look at elemental composition and molecular bonds. The core analytical aspect of this technique for elemental analysis is similar to the widely used atomic emission spectroscopy. In this technique the sample is subjected to a laser beam pulse where some of the sample is ablated, and the emission from the plasma of the ablated product is recorded and analyzed. LIBS is typically used on samples directly, without sample preparation procedures. However, for quantitative analysis this can be difficult and time consuming if the analyte of interest is not present homogenously within the sample. This invention allows one to utilize the advantages of fast analysis by LIBS on analytes by extracting them in a homogenous matrix.
The techniques developed in biological analysis lend themselves to high throughput analysis. In these methods the high throughput is obtained in two ways, first by analyzing arrays of samples (solids or liquids) where the analyte of interest is present homogenously in the sample or each array element, and second by automating the sample preparation. As an example, microarray and microwell formats are routinely used for biological samples and are then analyzed by optical scanners (by looking for fluorescence, luminescence and absorption/transmission changes and quantifying these). Typical microwell formats have 24, 96, 384, 1536 or more wells in an area of about 8 cm×13 cm. Such plates can be read by the optical scanners in a matter of minutes. Solid microarrays may have thousands of analytical spots on a plate. Further, standards may occupy some of the spots or wells of these plates so that they are all read almost simultaneously (within minutes) avoiding temporal drift.
In addition to read the samples rapidly, it is preferable to automate the sample preparation procedures which require repetitive steps of mixing various liquids, filtration, pipetting, and weighing. The purpose of this invention is to enable high throughput analysis of sample arrays that can be analyzed by LIBS.
One object of this invention is to analyze liquid samples by LIBS.
Another object of this invention is to extract the analytes of interest from a sample into a homogenous matrix, and subject arrays formed from the said matrices to analysis by LIBS.
Yet another object of the present invention is to demonstrate that environmental and industrial hygiene sample arrays can be measured at high throughputs using LIBS.
Another objective of this invention is to enable processes so that environmental and industrial hygiene sample arrays could be prepared with high degree of automation which are ready for analysis by LIBS.
Yet another objective is to be able to make multiwall arrays for compositional analysis.